1. Field of the Invention
This invention relates to a method and apparatus for direct casting of metal alloys from molten metal to continuous sheet or strip product. More particularly, it relates to synchronizing the speed of the cast strip to maintain strip integrity for subsequent operations.
2. Background
There is a wide variety of methods and apparatus proposed for the production of directly cast strip. Typically, such methods are those which include spraying molten metal through a metering orifice across a gap to a rapidly moving quenching surface, such as a wheel or continuous belt; methods which partially submerge a rotating quenching surface into a pool of molten metal; methods which use horizontal link belts as quenching substrates upon which molten metal flows for solidification; and methods of casting with twin casting rolls having a pool of molten metal therebetween. Some of the processes have the capability of casting the strip horizontally and others for casting the strip in a vertical direction.
Although none of the direct casting processes proposed are known to have developed into commercial processes, each is potentially capable of producing an as-cast near net shape sheet or strip product. That product is then subjected to downstream operations to develop the final sheet or strip product. Such operations may include cold rolling, skinpass rolling, annealing and pickling, as well as cutting and slitting operations. U.S. Pat. No. 5,045,124, issued Sep. 3, 1991, discloses a process wherein the cast strip is thereafter skinpass rolled. Such downstream operations frequently may include a pair of rolls, such as pinch rolls, which may be used for such skinpass rolling or for cooling the cast strip, reducing its gauge, or smoothing the top and bottom surfaces of the strip. Furthermore, it has been found that through the use of a pinch roll set, the tension and compressive forces created further downstream by subsequent operations can be isolated from disturbing the casting process upstream. This is especially important when continuously transporting hot strip from a casting wheel in a manner such as that disclosed in U.S. Pat. No. 5,293,926, issued Mar. 15, 1994. One problem identified for many of the various processes is that the as-cast strip may have an uneven or rough top or bottom surface which creates speed disturbances in the pinch roll and results in buckles or breaks in the as-cast strip upstream toward the caster.
What is needed is a method and apparatus for direct casting sheet and strip having surface quality comparable to or better than conventionally-produced strip to enhance commercialization of such processes. Such a method and apparatus should be able to produce sheet and strip products by transporting the as-cast strip from the casting surface or surfaces to the pinch roll without the occurrence of breaks or buckles in the strip therebetween. The direct cast strip should have good surface quality, edges and structure and properties at least as good as conventionally-cast strip.